Partisans on both sides have a tendency to want to believe that their party's troubles can be solved by moving away from the center and instead locking down the base. It's usually not true. In this case, however, there seems to be strong evidence that an unenthusiastic base is in fact the Democrats' biggest problem.

A new Democracy Corps poll shows that voters who are most likely to vote in November are far more opposed to the Democrats than voters who aren't (Democracy Corps calls the latter group "Drop-Off Voters"). Likely voters are split, 47-48, on whether President Obama is doing a good job. Drop-off voters overwhelmingly (59-35) approve of his job performance. Likely voters slightly (47-44) think they'll vote for a Republican for Congress. Drop-off voters overwhelmingly (55-30) would vote for a Democrat.

A Gallup poll shows the same dynamic. Here's a graph of the enthusiasm gap between Republicans and Democrats:

How does this dynamic translate to individual races? David Jarman juxtaposes two recent polls of the Pennsylvania Senate race. Among registered voters, Arlen Specter leads Pat Toomey by 7 points. But among likely voters, Toomey leads by 9:

Democrats face an enormous problem here. The electorate that shows up in November could be far more Republican than the electorate as a whole. In these circumstances, it seems like the party's number one imperative has to be shoring up the base and giving its voters a reason to go to the polls in November. You can probably guess what I think that means about the political logic of passing health care reform.